Record carrier and apparatus for scanning the record carrier

ABSTRACT

A record carrier has a servo track ( 4 ) indicating an information track ( 9 ) intended for recording information blocks. The servo track ( 4 ) has a periodic variation of a physical parameter at a predetermined frequency and modulated parts for encoding position information at regular intervals. The modulated parts start with a bit sync element and are of a data type having a data bit element or of a word sync type having a word sync element. The bit sync element, word sync element and the data bit element being modulated according to a same predetermined type of modulation of the periodic variation. All distances between two adjacent of the elements constituting the modulated parts are unique.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a record carrier comprising a servo trackindicating an information track intended for recording informationblocks represented by marks, said servo track having a periodicvariation of a physical parameter at a predetermined frequency andmodulated parts for encoding position information at regular intervals,the modulated parts comprising at least one of a bit sync element, adata bit element or a word sync element, said elements being modulatedaccording to a same predetermined type of modulation of the periodicvariation.

The invention further relates to a recording and/or playback devicecomprising means for writing and/or reading information blocks in aninformation track on a record carrier comprising a servo trackindicating the information track, recording and/or playback devicefurther comprising means for scanning the servo track, and demodulationmeans for retrieving position information from a signal generated by avariation of a physical parameter of the servo track at a predeterminedfrequency, said servo track having modulated parts for encoding positioninformation at regular intervals, the modulated parts comprising atleast one of a bit sync element, a data bit element or a word syncelement, said elements being modulated according to a same predeterminedtype of modulation of the periodic variation.

The invention further relates to a method for manufacturing the recordcarrier.

2. Description of the Related Art

A record carrier and device for reading and/or writing information areknown from International Patent Application No. WO 00/43996,corresponding to U.S. Pat. No. 6,765,861 (PHN 17323). The information tobe recorded is encoded into an information signal which includes addresscodes and is subdivided in accordance with the address codes intoinformation blocks. The record carrier is of a recordable type and has aservo track, usually called pre-groove, for causing servo signals to begenerated when scanning the track. A physical parameter, e.g., theradial position, of the pre-groove periodically varies at apredetermined frequency constituting a so-called wobble. During thescanning of the track, this wobble leads to a variation of the radialtracking servo signals and a wobble signal can be generated. The wobbleis modulated according to a type of modulation using phase modulationfor encoding position information. The phase modulation or frequencymodulation used for encoding digital position information is selected tominimally disturb the component of the predetermined frequency in thewobble signal, because that component is used to control the recordingspeed. Hence, a majority of the periodic variations needs to benon-modulated, i.e., having the zero crossings not shifted from thenominal positions. During recording, the position information isretrieved from the wobble signal and is used for positioning theinformation blocks by keeping a predefined relation between the addresscodes in the information blocks and the position information. Theaddresses are encoded in modulated parts of the wobble starting with abit sync element followed by either a word sync element or a data bitelement.

A problem of the known system is that detection of the various elementsis not reliable.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a record carrier and devicein which the synchronization is more reliable.

According to the invention, a record carrier as defined in the openingparagraph is characterized in that all distances between two adjacent ofsaid modulated elements are unique. Further, the recording and/orplayback device, as described in the opening paragraph, is characterizedin that the demodulation means comprise means for detecting a type ofthe modulated parts by determining the unique distance between precedingand/or following modulated elements. The invention is based on thefollowing recognition. In both the DVD+RW and the new format, theaddress information in the wobble is stored by having short modulatedmarks in a predominantly single-tone wobble. In DVD+RW, the modulatedmarks are inverted wobbles (PSK modulation), while in the new format,the modulated marks are of the MSK (minimum shift keying) type. It is anadvantage to use only one type of modulated mark, because then only onetype of modulated mark needs to be detected, which is simple.Information is then stored in the combination of multiple marks. Themodulated marks are used to indicate bit sync, word sync, data ONE, anddata ZERO. From the detection of a single mark, no information can beretrieved without having information also on other marks because it isnot known whether the detected mark indicates (part of) a bit sync, wordsync, data ONE, or data ZERO. The solution of this invention is to makethe distance between each pair of adjacent modulated marks unique, sothat from the distance between two subsequent modulated marks, allrelevant information can be retrieved. The solution of this inventionthus makes it possible to have very simple detection: detect singlemodulated marks and the distance between adjacent marks. Hence, reliabledetection in combination with minimal disturbance of the periodicvariations is achieved by selecting unique distances and using a singlemodulated element for the bit sync, data bit and word sync elements.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from andelucidated further with reference to the embodiments described by way ofexample in the following description and with reference to theaccompanying drawings, in which:

FIG. 1 a shows a record carrier with a servo track (top view);

FIG. 1 b shows a servo track (cross section);

FIG. 1 c shows a wobble of a servo track (detail);

FIG. 1 d shows a further wobble of a servo track (detail);

FIG. 2 shows bi-phase wobble modulation;

FIG. 3 shows MSK wobble modulation;

FIG. 4 shows a modulation scheme including unique distances;

FIG. 5 shows a device for reading information blocks; and

FIG. 6 shows a device for writing information blocks.

In the Figures, elements which correspond to elements already describedhave the same reference numerals.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 a shows a disc-shaped record carrier 1 provided with a track 9intended for recording and a central hole 10. The track 9 is arranged inaccordance with a spiral pattern of windings 3. FIG. 1 b is across-section of the record carrier 1 taken on the line b—b in FIG. 1 a,in which a transparent substrate 5 is provided with a recording layer 6and a protective layer 7. The recording layer 6 may be opticallywritable, for example, via phase change, or magneto-optically writableby a device for writing information, such as the known CD-Rewritable orCD-Recordable. The recording layer may also be provided with informationvia a production process, in which first a master disc is made which issubsequently multiplied through pressing. The information is organizedin information blocks and is represented by optically readable marks inthe form of a succession of areas reflecting much radiation and littleradiation such as, for example, a succession of pits of differentlengths in a CD. In one embodiment, the track 9 on the record carrier ofa rewritable type is indicated by a servo-pattern which is providedduring manufacture of the blank record carrier. The servo-pattern isformed, for example, by a pre-groove 4 which enables a write head tofollow the track 9 during scanning. The pre-groove 4 may be implementedas a deeper or a raised part, or as a material property deviating fromits ambience. Alternatively, the servo-pattern may consist of analternation of elevated and deeper windings, referred to as land andgroove patterns, with a transition from land to groove or vice versataking place per winding. FIGS. 1 c and 1 d show two examples of aperiodical variation of a physical parameter of the pre-groove, calledwobble. FIG. 1 c shows variation of the lateral position, and FIG. 1 dshows variation of the width. This wobble produces a wobble signal in atracking servo-sensor. The wobble is, for example, frequency-modulated,and position information, such as an address, a time code or windinginformation, is coded in the modulation. A description of a rewritableCD system which is provided with position information in such a way canbe found in U.S. Pat. No. 4,901,300 (PHN 12,398). A servo-pattern mayalso consist of, for example, regularly distributed sub-patterns whichperiodically cause tracking signals. Further, the servo-pattern mayinclude modifications of the land area beside the pre-groove, e.g., anundulating pre-groove having land pre-pits in a specific pattern forencoding position information like in DVD-RW.

The variation of the servo track includes relatively large parts ofmonotone wobble, so-called non-modulated parts. Further the servo trackhas relatively short parts where the frequency and/or phase of thewobble deviates from the predetermined wobble frequency, calledmodulated parts. In this document, any servo-pattern of a periodicnature in combination with any additional elements encoding informationis referred to as a servo track having a periodic variation of aphysical parameter at a predetermined frequency, or wobble, that hasmodulated parts.

FIG. 2 shows bi-phase wobble modulation. An upper trace shows the wobblemodulation for a word sync pattern, a second and third trace show thewobble modulations for data bits of the address, the total modulationbeing called Address In Pre-groove (ADIP). Predetermined phase patternsare used for indicating a synchronizing symbol (ADIP bit sync) and asynchronization of the full address word (ADIP word sync), and for therespective data bits (ADIP Data=‘0’, and ADIP data=‘1’). The ADIP bitsync is indicated by a single inverted wobble (wobble # 0). The ADIPword sync is indicated by three inverted wobbles directly following theADIP bit sync, whereas data bits have non-inverted wobbles in this area(wobble # 1 to 3). An ADIP Data area comprises a number of wobbleperiods assigned to represent one data bit, in FIG. 2, the wobbleperiods numbered 4 up to 7 (=wobble # 4 to 7). The wobble phase in firsthalf of the ADIP Data area is inverse to the wobble phase in the secondhalf of the area. As such, each bit is represented by two sub-areashaving different phases of the wobble, i.e., called bi-phase. Data bitsare modulated as follows: ADIP Data=‘0’ is represented by 2 non-invertedwobbles followed by two inverted wobbles, and ADIP data=‘1’, vice versa.In this embodiment, the modulation for data bits is fully symmetrical,giving equal error probability for both data bit values. However, othercombinations of wobbles and inverted wobbles, or other phase values maybe used. In an embodiment, a predetermined modulation is used after aADIP Word Sync, indicating ‘empty’, instead of a data bit. Monotonewobbles may be used after the first data bit, or further data bits maybe encoded thereafter. Preferably, a large majority of the wobbles isnot modulated (i.e., has the nominal phase) for ensuring an easy lockand a stable output of a PLL in a detector; in this embodiment, the 8possibly modulated wobbles are followed by 85 not modulated (i.e.,monotone) wobbles (wobble # 8 to 92). The output frequency of the PLLhas to be as stable as possible, because during writing, the write clockis derived from the PLL output.

FIG. 3 shows MSK wobble modulation. The Minimum Shift Keying (MSK)modulation uses a first pattern 31 for transferring a first bit valueand a second pattern 32 for transferring a second bit value. Furthercombinations of the patterns 31, 32 may be used to transfersynchronization information. Each MSK pattern has a central part of atleast one full wobble period; in the first pattern, the central part 34is non-inverted, while in the second pattern, the central part 37 isinverted. Each MSK pattern further has a starting part and an endingpart. The left MSK pattern has a starting part 33 and an ending part 35just being a single wobble period. The right MSK pattern has a startingpart 36, which inverts the phase by having a frequency of 1.5 times thewobble frequency, i.e., by having 3 half sine periods within one wobblefrequency period. The ending part is similar to re-invert the phase tothe non-inverted state. Detection of MSK data bits is primarily based onthe detection of the central part, because both central parts exhibitthe maximum difference between the two patterns. In addition, thedifference of the not-modulated starting part 33 and modulated startingpart 36, and the not-modulated ending part 35 and modulated ending part38 can be exploited for detection, the total length of these differencesis estimated to have 50% of effective strength of detection whencompared to the central part. The MSK encoding can be used to encodeaddress bits in a pre-groove wobble, but the pre-groove wobble needs tobe not modulated for the majority of wobble periods. The large majorityof not-modulated wobbles is needed for reliably controlling the rotationspeed of the disc and/or the write clock of the recording process.

FIG. 4 shows a modulation scheme with split word sync based on the MSKwobble modulation. In each cell of the matrix shown, a zero indicates anot-modulated wobble, a one indicates a starting part of 1.5 wobble toinvert the phase, a two indicates an inverted wobble, and a threeindicates an ending part of 1.5 wobble to re-invert the phase to thenormal state, as described above with reference to FIG. 3. In each rowof the matrix, 56 consecutive wobbles are indicated (columns 37–54 allbeing zero), and each row starts with a bit sync element in columns 0,1, 2. A total ADIP address word comprises 83 rows, and the rows arenumbered according to their ADIP bit number. The ADIP bits numbered 0,2, 4, 6 and 8, 13, 18, etc., are isolated bit syncs (40, 41). The ADIPword includes several word sync elements, which all comprise two partialelements separated by a number of not-modulated wobbles. Such syncelements are referred to as split word sync. In ADIP bit 1, there is afirst split word sync element called sync0, and in ADIP bits 3, 5, 7there are three further split word sync elements sync1, sync2 and sync3.All split word sync elements have a different location for maximumreliability of detection. Starting at ADIP bit 8, there is a repetitivepattern of 5 rows consisting of one isolated bit sync followed by 4 databits; the values of the data bit elements in FIG. 4 being arbitraryexamples. Hence, in total, 13×4=52 data bits are available in the ADIPaddress word.

In the new format, we have the following specific implementation. EachADIP unit has a length of 56 wobbles. Seven different types of ADIPunits exist. The following unique distances occur between differentadjacent elements:

distance of 10 wobbles: between the two elements of 1 of the 4 wordsyncs distance of 12 wobbles: between bit sync and data ONE elementdistance of 14 wobbles: between bit sync and data ZERO element distanceof 16 wobbles: between bit sync and first element of sync0 distance of18 wobbles: between bit sync and first element of sync1 distance of 20wobbles: between bit sync and first element of sync2 distance of 22wobbles: between bit sync and first element of sync3 distance of 24wobbles: between second element of sync3 and bit sync of next ADIP unitdistance of 26 wobbles: between second element of sync2 and bit sync ofnext ADIP unit distance of 28 wobbles: between second element of sync1and bit sync of next ADIP unit distance of 30 wobbles: between secondelement of sync0 and bit sync of next ADIP unit distance of 42 wobbles:between ZERO element and bit sync of next ADIP unit distance of 44wobbles: between ONE element and bit sync of next ADIP unit distance of56 wobbles: between bit sync and bit sync of next ADIP unitNo other distances between 2 adjacent elements occur in the format. So,from the distance between 2 adjacent MSK elements, one can directlyderive the meaning of the elements. Note that all distances are largerthan 10, so no 2 elements are close together which is an advantage forreducing the PLL distortion. Note that all distances are even, if one ofthe elements is shifted by 1 wobble because of misdetection one candetect this error (but not correct it). Note that the unique aspect islimited to the adjacent elements, the distance between non-adjacentelements is not unique. For example, the distance 26 also occurs betweenthe bit sync and the second element of sync0 (because 26=16+10), but inthis case, there is another element (the first element of sync0) inbetween. Note that the distance 10 is somewhat special, it occurs forall 4 word syncs (sync0, . . . , sync3). The disadvantage is that fromdetecting distance 10, one does not know which word sync is detected.The advantage is that one can use 1 type of detection for all 4 wordsyncs.

FIG. 5 shows a reading device for scanning a record carrier 1. Writingand reading of information on optical discs and formatting, errorcorrecting and channel coding rules, are well-known in the art, e.g.,from the CD system. The apparatus of FIG. 5 is arranged for reading therecord carrier 1, this record carrier being identical to the recordcarrier shown in FIGS. 1 a–1 d. The reading device is provided with aread head 52 for scanning the track on the record carrier and readcontrol means comprising drive unit 55 for rotating the record carrier1, a read circuit 53, for example, comprising a channel decoder and anerror corrector, tracking unit 51 and a system control unit 56. The readhead comprises optical elements of the usual type for generating aradiation spot 66 focused on a track of the recording layer of therecord carrier via a radiation beam 65 guided through optical elements.The radiation beam 65 is generated by a radiation source, e.g., a laserdiode. The read head further comprises a focusing actuator for focusingthe radiation beam 65 on the recording layer and a tracking actuator 59for fine positioning of the spot 66 in radial direction on the center ofthe track. The apparatus has a positioning unit 54 for coarselypositioning the read head 52 in the radial direction on the track. Thetracking actuator 59 may comprise coils for radially moving an opticalelement or may be arranged for changing the angle of a reflectingelement on a movable part of the read head or on a part on a fixedposition in the case part of the optical system is mounted on a fixedposition. The radiation reflected by the recording layer is detected bya detector of a usual type, e.g., a four-quadrant diode, for generatingdetector signals 57 including a read signal, a tracking error and afocusing error signal. The tracking unit 51 is coupled to the read headfor receiving the tracking error signal from the read head andcontrolling the tracking actuator 59. During reading, the read signal isconverted into output information, indicated by arrow 64, in the readcircuit 53. The apparatus is provided with a demodulator 50 fordetecting and retrieving address information from the wobble signalincluded in the detector signals 57 when scanning the servo track of therecord carrier. The device is further provided with a system controlunit 56 for receiving commands from a controlling computer system orfrom a user, and for controlling the apparatus via control lines 58,e.g., a system bus connected to the drive unit 55, the positioning unit54, the demodulator 50, the tracking unit 51 and the read circuit 53. Tothis end, the system control unit comprises control circuitry, forexample, a microprocessor, a program memory and control gates, forperforming the procedures described below. The system control unit 56may also be implemented as a state machine in logic circuits. The readdevice is arranged for reading a disc having tracks having a periodicvariation, e.g., a continuous wobble. The read control unit is arrangedfor detecting the periodic variations and for reading, in dependencethereon, a predetermined amount of data from the track. In particular,the demodulator 50 is arranged for reading position information from themodulated signal derived from the modulated wobble. The demodulator 50has a detection unit for detecting modulated wobbles starting at the bitsync elements in the wobble signal which arrive after a long sequence ofnon-modulated wobbles. The demodulator further has a word detection unitfor retrieving the words of address information based on the word syncelements. The beginning of such a word is detected from a wordsynchronization signal after the bit sync element. The value of a databit is detected based on the data bit elements encoded by modulatedwobbles. Further, the device has a synchronization unit 67 for detectingthe unique distances between modulated elements. In the modulationscheme described above with reference to FIG. 4, all modulated elementsare separated by a unique interval of not-modulated periodic variations.The synchronization unit 67 detects the modulated elements at the uniquedistances, and from the result, detects the bit sync, word sync, or databit element. In a preferred embodiment, the demodulator 50 andsynchronization unit 67 share a filter unit for detecting one singletype of modulated element, in particular, in the case that all modulatedparts of the data bits, the word sync element and the bit sync elementare equal.

FIG. 6 shows a device for writing information on a record carrieraccording to the invention of a type which is (re)writable in, forexample, a magneto-optical or optical manner (via phase change or dye)by means of a beam 65 of electromagnetic radiation. The writing deviceis also equipped for reading and comprises the same elements as theapparatus for reading described above with FIG. 5, except that thewriting device has a write/read head 62 and recording control meanswhich comprises the same elements as the read control means, except fora write circuit 60 that comprises, for example, a formatter, an errorencoder and a channel encoder. The write/read head 62 has the samefunction as the read head 52 together with a write function and iscoupled to the write circuit 60. The information presented to the inputof the write circuit 60 (indicated by the arrow 63) is distributed overlogical and physical sectors according to formatting and encoding rulesand converted into a write signal 61 for the write/read head 62. Thesystem control unit 56 is arranged for controlling the write circuit 60and for performing the position information recovery and positioningprocedure as described above for the reading apparatus. During thewriting operation, marks representing the information are formed on therecord carrier. The recording control means is arranged for detectingthe periodic variations, for example, by locking a phase-locked loop tothe periodicity thereof. The demodulator 50 and the synchronization unit67 are described above with reference to FIG. 5.

Although the invention has been explained by embodiments using a wobblemodulation, any other suitable parameter of the track may be modulated,e.g., the track width. Also, for the record carrier, an optical disc hasbeen described, but other media, such as a magnetic disc or tape, may beused. It is noted, that in this document, the word ‘comprising’ does notexclude the presence of elements or steps other than those listed, andthe word ‘a’ or ‘an’ preceding an element does not exclude the presenceof a plurality of such elements, that any reference signs do not limitthe scope of the claims, that the invention may be implemented by meansof both hardware and software, and that several ‘means’ may berepresented by the same item of hardware. Further, the scope of theinvention is not limited to the embodiments, and the invention lies ineach and every novel feature or combination of features described above.

1. A record carrier comprising a servo track indicating an informationtrack intended for recording information blocks represented by marks,said servo track having a periodic variation of a physical parameter ata predetermined frequency and modulated parts for encoding positioninformation at regular intervals, the modulated parts comprising atleast one of a bit sync element, a data bit element or a word syncelement, said elements being modulated according to a same predeterminedtype of modulation of the periodic variation, characterized in that alldistances between two adjacent of said modulated elements are unique. 2.The record carrier as claimed in claim 1, wherein the predetermined typeof modulation is minimum shift keying modulation of the periodicvariation.
 3. The record carrier as claimed in claim 1, wherein amodulated part of a word sync type has two modulated elements at afurther unique distance.
 4. The record carrier as claimed in claim 3,wherein the further unique distance within the word sync type is 10periods and the unique distances are larger than 10 periods of theperiodic variation.
 5. The record carrier as claimed in claim 1, whereinall unique distances are an even value of periods of the periodicvariation.
 6. The record carrier as claimed in claim 1, wherein allmodulated elements are equal.
 7. A recording and/or playback devicecomprising means for writing and/or reading information blocks in aninformation track on a record carrier comprising a servo trackindicating the information track, said recording and/or playback devicecomprising means for scanning the servo track and demodulation means forretrieving position information from a signal generated by a variationof a physical parameter of the servo track at a predetermined frequency,said servo track having modulated parts for encoding positioninformation at regular intervals, the modulated parts comprising atleast one of a bit sync element, a data bit element or a word syncelement, said elements being modulated according to a same predeterminedtype of modulation of the periodic variation, characterized in that thedemodulation means comprises means for detecting a type of the modulatedparts by determining a unique distance between preceding and/orfollowing modulated elements.
 8. The recording and/or playback device asclaimed in claim 7, wherein the means for detecting the type of themodulated parts detects the unique distance from modulated elements thatare separated by an interval of not-modulated periodic variations.